This invention relates to a wrapping machine, and more particularly to a wrapping machine in which seam sealing of wrapping films at its both sides can be done by means of a conductive band or wire (in the following, it is called "heat sealing band"), which is put on pulleys or wheels which are held to horizontal pivotal shafts.
Heretofore, as shown in FIG. 7A, the seam sealing of wrapping films at its both sides has been done by means of heat sealing wheels 91, and 91 which are held to vertical pivotal shafts. Herein reference numerals 92, and 93 designate grip belts for feeding film and article with nipping these, reference numeral 94 a former (machine which forms to give shape to the film).
However, in the case of a machine shown in FIG. 7A, there were defects that heat sealing wheels 91, and 91 contacted only a part of wrapping film in a very short time interval as shown at t1 in FIG. 6, so that the surface temperature of the heat sealing wheel should have been made higher. Therefore, in order to transmit heat to the seam sealed part of the wrapping film, the surface temperature thereof should have been made higher than the melting point m of packing film as shown with line 95 in FIG. 6. In the case of thick film or laminated film, the necessity for such high temperature was particularly important. These temperatures can be reduced by reducing the rotation speed of the heat sealing wheels 91, and 91. However, in that case, the efficiency became worse.
For the above mentioned reason, a machine in which heat sealing bands 97, and 97 are mounted about vertical shafts has been proposed. However, in that case, the length of the former and wrapping material became disadvantageously longer as shown by length l.sub.1 in FIG. 8A.
As shown in FIGS. 7A and 8A, as the heating surfaces of heat sealing wheels 91, and 91 or that of heat sealing bands 97, and 97 was vertical, the heat sealing parts of two films should be put in such a shape as to put one's hands flat together. And the ends of the films whose ends were put in such a shape as to put one's hands flat together projected slightly out of a space between two boards 98 as shown in FIG. 5C, in such a degree that the ends of the films can be held between heat sealing wheels 91, and 91, or heat sealing band 97, and 97, shown by length l.sub.2, the length l.sub.2 is larger than length l.sub.3 of the present invention shown in FIG. 5B, so that films of considerable length were necessary and thereby a part of the films was wasted. And it was necessary to arrange a bearing member facing the heat sealing band. Further, when placing the films whose ends were put in such shapes as to put one's hand flat together along an external form of an article, another folding machine for folding films whose ends were put in such shapes as to put one's hands flat together should have been arranged behind the heat sealing band.
Further, in a conventional machine, as above mentioned, heat sealing wheels 91, and 91 or heat sealing bands 97, and 97 were held to vertical shafts 90, and 90, or vertical shafts 96, and 96, in which heating surface of heat sealing wheels 91, and 91 or that of heat sealing bands 97, and 97 were rotated about vertical axes. Therefore, it was impossible to place conveyers for transferring packages, that is, grip belt 92, and 93 along heat sealing wheels 91 or heat sealing bands 97. Therefore, grip belts 92, and 93 which consist of a pair of conveyers for transferring articles cannot have been arranged along heat sealing bands, and should be provided at the place determined according following process. Therefore, the total length of machine became longer than length l, and l.sub.1 as shown in FIGS. 7A and 8A.
Further in the conventional machine, as the heat sealing band contacted with only the sealing part of the films whose ends were put in such shapes as to put one's hands flat together with pressure between the heat sealing bands, or between a heat sealing band and a bearing board acting on the sealing part, the feeding direction of the wrapping was unstable, and therefore it was necessary to provide a guide plate for correcting at both sides.
On the other hand, in constructing a heat sealing band, it was common that the electrically insulating section was made longer than the electrically conducting section, and thereby useless electric transmission was lessened to the utmost, so as to transmit effective maximum power. However, in the conventional machine, as the heat sealing band was put on wheels held to vertical shafts, for making a longer electrically insulating section of the heat sealing band, it was necessary to extend the length of the heat sealing band in the lateral direction. But, in that case, there were mounting and safety problems, by which an electrically insulating section cannot be longer without some restriction, and therefore there was a disadvantage that the length of the electrically insulating section was itself restricted.